PROJECT SUMMARY/ABSTRACT: This is a P41 renewal proposal to continue the National Biomedical Center for Advance ESR Technology (ACERT). Four principal areas of Technology Research and Development (TR&D) will be emphasized. They consist of 1) High-Sensitivity Pulse Dipolar ESR Spectroscopy and 2D-FT ESR from X to Ka Band; 2) Electron Spin Resonance with Ultra-High Sensitivity for Very Small Biological Samples; 3) Developments in High Frequency ESR, and 4) Improved Computational Methods for ESR Analysis and Spectral Processing. Extensive Driven Biomedical Projects and other collaborations with biomedical researchers will greatly benefit from these TR&Ds, which in turn are driven by the DBP needs for the new and improved ESR technologies. Thus, there is an important synergism amongst the TR&Ds and the DBPs. The technologies being developed at ACERT are in many respects unique in the world. The extensive DBP's and collaborative/service projects at ACERT will continue to bring these modern ESR methods to the forefront of biomedical research, especially as the additional challenges are addressed in the TR&D's. This includes our plans to increase spectral sensitivity in our ACERT spectrometers, for which the demands continue to grow. The plans for dissemination and training address the need to bring these new technologies to other laboratories in the USA and elsewhere in addition to making the facilities available to outside scientists, publishing and advertising the results of the Center and running workshops on the new methodologies.